JPS5916835B2 - How to paint steel structures - Google Patents

Description

[Detailed Description of the Invention] Regarding the method of painting steel structures of the present invention, more details are given below.
This invention relates to a method for painting steel structures with a two-component paint that has curability 5 even at low temperatures of 20°C to +5°C.

In recent years, heavy-duty anti-corrosion coating using epoxy paint has been used to protect large steel structures such as on-shore structures and offshore structures, especially plants and pipelines, and has achieved many results. .

However, due to the industrial period, painting has become extremely cold, and we are often forced to paint in cold regions. Conventionally,
It was common knowledge that painting should not be performed in a low temperature atmosphere of 5°C or lower. The reason for this is that in low-temperature environments, the epoxy-polyamine or epoxy-polyamide two-component paints that are often used in i5 layer anti-corrosion coatings cure slowly.
This is because it is difficult to cure the coating to such an extent that, for example, a person can walk on the coating within the practically required 24 hours. On the other hand, a composition using an alkanolamine-modified epoxy resin and a polyisocyanate is known as an epoxy paint that cures even at a temperature of about 5°C.

However, conventionally known alkano-35-lamine-modified epoxy resin/polyisocyanate compositions have a low nonvolatile content, at most 60% by weight, and have a film thickness of 100 microns or more, which is required as a heavy-duty anticorrosive coating. It was very difficult to form this in one coat. In addition, since the non-volatile content is low at 60% by weight or less, solvent volatilization is slow in low-temperature atmospheres, resulting in solvent remaining in the coating film, resulting in drawbacks such as reduced adhesion and water resistance of the coating film. was. Furthermore, when conventional alkanolamine-modified epoxy resin/polyisocyanate compositions are coated with a non-volatile content of 70% by weight or more, the viscosity of the composition increases, making it difficult to use simple methods such as airless spraying or brushing. Painting was not possible, and painting had to be done using special, large-scale equipment such as two-component spray equipment. For this reason, there has been a strong desire to develop a method for easily applying a paint with excellent anticorrosion properties in a low-temperature atmosphere. In order to solve all of the above problems, the present inventors have made the present invention as a result of intensive research.
When painting steel structures in a low-temperature atmosphere of ℃, the following main components are used:
Alkanolamine modified epoxy resin (8) 2,21-
or 2,41- or 4,41-diisocyanate diphenylmethane or modified products thereof.

, and the mixing ratio of the components (A) and (8) is 1:0.5 to 1:0.5 expressed as the equivalent ratio of hydroxyl group to isocyanate group.
1.5, and the coating method for steel structures comprises forming a film thickness of 100 microns or more in one coating using a two-component paint with a non-volatile content of 70% by weight or more during coating.

Furthermore, when painting marine structures such as sea berths, offshore oil drilling rigs, quay cranes, and seashore bridges where steel structures are exposed to seawater spray or sea salt particles, a primer is applied before applying the two-component paint. There is a method for painting steel structures that involves applying an inorganic zinc primer. ．． The present invention will be explained in detail below. First, as a two-component paint, the vehicle is a 4-alkanolamine-modified epoxy resin,
(B) A two-component paint whose main component is 2,2'-, 2,4' or 4,4'-diisocyanate diphenylmethane or modified products thereof, and component 6, the alkanolamine-modified epoxy resin, has a molecular weight of Use one with a value of 650 or less.

When the molecular weight exceeds '650, the viscosity of the paint increases rapidly, especially in a low temperature atmosphere of -2'C to +5°C.
When the amount exceeds % by weight, it becomes impossible to paint using simple methods such as airless spraying or... The alkanolamine used for modification has an alkanol group with 2 to 4 carbon atoms.
In particular, those modified with diethanolamine or diisopropanolamine can be suitably used for coating marine structures.

As the epoxy resin, there can be used commercially available epoxy resins having a suitable molecular weight range, such as shrimp chlorohydrin-bisphenol A ether type, novolac type, and other alicyclic resins. The reaction between alkanolamine and epoxy resin in making alkanolamine-modified epoxy resin is carried out by dissolving the epoxy resin in a solvent such as methyl isobutyl ketone, xylene, toluene, etc.
It is obtained by reacting with an alkanolamine at a temperature of 100° C. for 1 to 3 hours. Next, as component (8), 2,2
1-, 2,41-, or 4,41-diisocyanate diphenylmethane (hereinafter collectively referred to as MDI)
(hereinafter referred to as modified MDI) or modified products thereof (hereinafter referred to as modified MDI) are used.

When using the above MD or modified MDI, -2 "C ~ +5
Sufficient curing can be obtained in a short time even at temperatures as low as ℃. It has been found that polyisocyanates other than MDI or modified MDI, such as tolylene diisocyanate or modified products thereof, are slow to cure at the low temperatures and cannot be put to practical use even when combined with the alkanolamine-modified epoxy resin. As the modified MDI, an adduct of MDI and trimethylolpropane can be preferably used. The alkanolamine-modified epoxy resin is converted into MDI or modified MD.
The mixing ratio is 1:0.5 to 1.5 expressed as an equivalent ratio of hydroxyl group to isocyanate group.

Outside this range, curing may be slow, or the properties of the formed coating film, particularly corrosion resistance, water resistance, bending resistance, etc. may deteriorate. The two-component paint used in the method of the present invention includes:
Pigments, fillers, additives, etc. can be added as appropriate.

First, as pigments, in addition to inorganic pigments such as titanium oxide, iron oxide black, iron oxide yellow, red iron oxide, etc., which are used in ordinary paints, organic pigments can also be used without any problem. Other barites,
Ordinary fillers such as calcium carbonate, clay, clay, and talc can also be used, and various additives can also be added depending on the purpose. For example, Molquilite 4P (manufactured by Kurita Industries, Ltd.), Zeolis T (manufactured by Bayer)
The use of water-absorbing agents such as these removes water contained in the paint, prevents the generation of carbon dioxide gas due to the reaction between isocyanate groups and water, and is effective as a measure to prevent foaming of the paint film.
Additionally, glass flakes, fiberglass, etc. may be added to increase the strength of the coating film or reduce water permeability.

The above-mentioned two-component paint is used for painting by uniformly mixing component A and component B immediately before use, but the non-volatile content of the two-component paint is used at 70% by weight or more during painting.

If it is less than 70% by weight, the solvent content will be too high and the solvent volatilization rate will be slow in a low-temperature atmosphere, resulting in the solvent remaining in the formed coating film and deteriorating the water resistance and adhesion of the coating film. cause.

Furthermore, if the nonvolatile content is low, it becomes difficult to obtain a film thickness of 100 microns or more in one coating, and a sufficient anticorrosion effect cannot be expected. Generally, the reaction of two-component paints starts from the moment they are mixed, so the pot life of the paint is limited, but the two-component paints used in the method of the present invention range from -20°C to +5°C.
It has a pot life of 3 hours or more in a low temperature atmosphere of ℃. At 15℃, it takes one and a half hours. As a heavy anti-corrosion paint,
The thickness of the formed two-component paint film must be 100 microns or more, and the thickness may be up to about 400 microns depending on the purpose.

In addition, when a primer is applied, it is desirable that the film thickness as a composite coating is 500 microns or less. In addition, in order to form a film thickness of 100 microns or more, 20 to 3
It is natural that it is disadvantageous in the coating process to apply a film with a thickness of 0 micron several times, but especially in a low temperature atmosphere as in the method of the present invention, a film thickness of 100 microns or more is formed in one application. This is absolutely necessary and required.

In the present invention, when applying the two-component paint, it may be applied directly to the steel structure after sandblasting or the like, but it is preferable to apply a primer from the viewpoint of anti-corrosion properties.

It is desirable to use a zinc primer as the primer. Particularly in the case of offshore structures where steel structures have stricter requirements regarding corrosion resistance, ethyl silicate, ammonium silicate, lithium silicate, etc. and metallic zinc powder are recommended for hardening properties and adhesion with top coats. It is necessary to use an inorganic zinc primer as a primer.

This is because in the case of marine structures, the paint film is often damaged for some reason after painting, and if an inorganic zinc primer is applied in such cases, even if the paint film is damaged, rust will not occur. , and sufficient corrosion resistance is maintained.
In addition, organic zinc primers containing epoxy resins, polyamide resins, and metal zinc powder as main components can also be used.

Both inorganic and organic zinc primers are applied by airless spraying, etc., and the film thickness is 50 to 100 microns for inorganic primers, preferably 70 to 80 microns, and 10 to 30 microns for organic primers. , preferably 10
~20 microns. Primers are applied on-site or, in some cases, at the factory. The method of the present invention makes it possible to paint in a low-temperature atmosphere of -20℃ to +5℃ using a simple method such as airless spraying or brushing, which was previously considered impossible, and the resulting coating film has excellent corrosion resistance and other properties. Provides products with excellent performance.

The method of the present invention is applied to buildings, machinery, storage tanks, bridges, land structures such as steel roads, sea berths, offshore oil drilling rigs, quayside cranes, and offshore bridges that are exposed to seawater spray or sea salt particles. It can be applied to a variety of uses, including the inner surface coating of marine structures, seawater intake pipes, natural gas transport pipes, slurry transport pipes, etc., and the outer surface coating of underground and soil-buried pipes, above-ground piping, and seawater piping.

In addition, in the past, it was difficult to repair the paint once it was painted in a low-temperature atmosphere due to the problems with the paint and painting equipment used as described above, but the method of the present invention can be applied to new installations for the above-mentioned applications. Of course, it can also be easily applied to repairs. Next, the present invention will be specifically explained with reference to Examples.

Parts and percentages are by weight unless otherwise specified. Example 1 Production of modified epoxy resin Epicoat 812 (epoxy resin manufactured by Shell Oil Co., Ltd.) 30 was placed in a three-necked flask equipped with a thermometer, stirrer, and reflux condenser.
Add 0 parts and 141.5 parts of methyl isobutyl ketone,
Epicoat 8 to methyl isobutyl ketone by heating to 0°C.
12 was completely dissolved.

After that, 266 parts of diisopropanolamine was added, and 10 parts of diisopropanolamine was added.
React at 0°C for 2 hours to obtain a non-volatile content of 80% and a viscosity of 8 ps.
(25°C), a diisopropanolamine-modified epoxy resin having a resin molecular weight of 570 and a hydroxyl equivalent of 95 was obtained. Preparation and coating of two-component paint A paint was prepared using the diisopropanolamine-modified epoxy resin described above with the following formulation.

The equivalent ratio of hydroxyl group:isocyanate group is 1:1, that is, the component (A
)/component (B) in a weight ratio of 100/69.0 and stirred uniformly. The nonvolatile content is 84.4%, the viscosity immediately after mixing is 10 ps (25 is C), and the viscosity at -20°C is 19
．． It was 3ps. Next, sandblasted 100x2
Apply the above mixed two-component paint to a 00x1.6I iron plate.
Airless spray at 20°C [using Graco Hydro Cat manufactured by Gray Co., Ltd.: pressure ratio 50:1 (secondary pressure 200 kg,
The primary pressure was 41<9/Crl).

The resulting coating film had a thickness of 125 μm and had no abnormalities in appearance such as bubbling or yellowing. Other examples regarding the performance of the coating film,
It is shown in Table 1 along with comparative examples. Example 2 Production of modified epoxy resin Chitsonox 22 was placed in the same three-necked flask as in Example 1.
1 (epoxy resin manufactured by Chitsuso Corporation) and 115.5 parts of methyl isobutyl ketone were added and heated to 50°C to completely dissolve Chissonox 221 in the methyl isobutyl ketone.

After that, 210 parts of diethanolamine was added and the reaction was carried out at 100°C for 2 hours, resulting in a non-volatile content of 80% and a viscosity of 7 ps (25
A diethanolamine-modified epoxy resin having a resin molecular weight of 460 and a hydroxyl equivalent of 77 was obtained. Preparation and coating of two-component paint A two-component paint was prepared in the same manner as in Example 1, except that the diisopropanolamine-modified epoxy resin in component (4) of Example 1 was replaced with the above diethanolamine-modified epoxy resin.

That is, they were mixed at a weight ratio of component 4/component (8) of 100/690 and an equivalent ratio of hydroxyl group:isocyanate group of 1:0.81. The non-volatile content of the paint is 84.4%, and the viscosity immediately after mixing is 10.
ps (25°C), and the viscosity at -10°C was 13.6ps. Next, I sandblasted 100x200x1.
Carbozing 11 (manufactured by Shinto Toyo Co., Ltd.) at 75 μm on the iron plate No. 6
After painting, the above two-component paint was applied at -10°C using an airless sprayer in the same manner as in Example 1. The resulting coating film had a thickness of 110 μm, and there were no abnormalities such as foaming or sagging. The performance of the coating film is shown in Table 1. Comparative Example 1 Production of modified epoxy resin In the same manner as in Example 1, 970 parts of Epicote 1001 (epoxy resin manufactured by Shell Oil Co., Ltd.) was mixed with 3 parts of methyl isobutyl ketone.
After that, 210 parts of diethanolamine was added and the reaction was carried out at 100°C for 2 hours, resulting in a non-volatile content of 79.
4%, viscosity 26.0ps (25°C), resin molecular weight 1
200, and a diethanolamine-modified epoxy resin having a hydroxyl equivalent of 90 was obtained.

Preparation and coating of two-component paint Component (4) of component 4 in Example 1 was prepared by replacing the diisopropanolamine 7-modified epoxy resin with the above diethanolamine-modified epoxy resin, but due to the high viscosity it could not be made into a paint. .

Therefore, it was diluted with a mixed solvent of xylene/methyl isobutyl ketone = 1/1 to adjust the nonvolatile content of component ^) to 50%. Diluted component (A)/component A3) weight ratio 216.
3/69.0, that is, the equivalent ratio of hydroxyl group:isocyanate group is 1
:0.95 and stirred uniformly. The nonvolatile content of the paint was 59.701). The viscosity immediately after mixing is 13.6
ps (257C) and 18.7ps at -10°C. Next, the two-component paint was applied to a 100 x 200 x 1.61001 iron plate, which had been sandblasted and coated with Carbozinc 11 as in Example 2, by airless spraying at -10°C. The resulting coating film had a thickness of 73μ, but had a sagging appearance. The performance of the coating film is shown in Table 1. Comparative Example 2 Preparation of Epoxy-Polyamine Paint An epoxy-polyamine paint conventionally used as a heavy duty anti-corrosion paint was prepared with the following formulation.

Similar to Example 2, sandblasting and Carbozinc 11
The epoxy-polyamine paint prepared by mixing the first component/second component in a weight ratio of 52.5/415 was applied to a 100 x 200 x 1.6 I iron plate coated with 75μ of the above-mentioned epoxy-polyamine paint by airless spraying at -10°C. However, curing was slow at -10°C, and it took 84 hours to cure to a level where walking was possible. The coating performance is shown in Table 1. Comparative Example 3 Preparation and coating of two-component paint Component (4) and component (8) prepared in Example 1 were mixed with hydroxyl groups:
The equivalent ratio of isocyanate groups is 1:1.6, that is, component (A)/
Component G3) was mixed in a weight ratio of 100/110 and stirred uniformly.

Non-volatile content is 86.7 (F6, viscosity immediately after mixing is 8 ps
(25°C), and the viscosity at -20°C was 19.3 ps. Next, apply the above mixed two-component paint to a sandblasted 100 x 200 x 1.6 iron plate by airless spraying with -2"C [using Graco Hydro Cat manufactured by Gray Co.:
Painting was carried out at a pressure ratio of 50:1 (secondary pressure 200 kg/CrlLl primary pressure 4 kg/d).

The resulting coating film had a thickness of 128μ. Table 1 shows the performance of the coating film. Comparative Example 4 Component (4) and component 03) prepared in Example 1 were combined with hydroxyl group:
Equivalent ratio of isocyanate groups 1:0.4, i.e. component (A)/
Component [F]) was mixed in a weight ratio of 100/28 and stirred uniformly.

The non-volatile content is 82.8 (fl), and the viscosity immediately after mixing is 17p.
s (25°C), and the viscosity at -20°C was 40 ps. Next, sandblasted 100x200x1.6? Airless spray the two-component paint mixed above at -20'C onto an iron plate (using Graco Hydro Cat manufactured by Gray Co., Ltd.).
Pressure ratio 50:1 (secondary pressure 200 kg/(-d, primary pressure 4
kg/d)].

The resulting coating film had a film thickness of 120μ. Table 1 shows the performance of the coating film. Comparative Example 5 Production of modified epoxy resin 300 parts of Araldite GY-260 (epoxy resin manufactured by Ciba Geigi) and 141.5 parts of methyl isobutyl ketone were placed in a three-necked flask equipped with a thermometer, a stirrer, and a reflux condenser. Araldite GY-260 was completely dissolved in methyl imbutyl ketone by heating to .degree.

After that, 266 parts of diisopropanolamine was added, and 10 parts of diisopropanolamine was added.
After reacting at 0°C for 2 hours, the non-volatile content was 8001) and the viscosity was 5.
A diisopropanolamine-modified epoxy resin having a resin molecular weight of 590 and a hydroxyl equivalent of 95 was obtained. Preparation and coating of two-component paint A paint was prepared using the diisopropanolamine-modified epoxy resin described above with the following formulation.

The equivalent ratio of hydroxyl group:isocyanate group is 1:1, that is, the component (4
)/component 03) in a coulometric ratio of 100/55 and stirred uniformly. The nonvolatile content is 67%, and the viscosity of C immediately after mixing is 13 ps (25 minutes C), and the viscosity at -20°C is 22 ps.
It was hot. Next, sandblasted 100x200x1
．． The above mixed two-component paint was sprayed onto a 6I iron plate at -20°C by airless spraying [using a Gracohydro cathode manufactured by Gray Co., Ltd.: pressure ratio 50:1 (secondary pressure 200 kg/d, primary pressure 4 kg/d)]. Painted.

The resulting coating film had a thickness of 70 μm. Table 1 shows the performance of the coating film. Comparative Example 6 Production of modified epoxy resin Epicoat 819 (epoxy resin manufactured by Shell Oil Co., Ltd.) 25 was placed in a three-necked flask equipped with a thermometer, stirrer, and reflux condenser.
Add 0 parts and 178 parts of methyl isobutyl ketone and heat at 50°C.
Heat to methyl isobu 4 methyl ketone and add Epicoat 8
19 was completely dissolved.

Then, 212 parts of diisopropanolamine was added and 10 parts of diisopropanolamine was added.
Reacted at 0℃ for 2 hours, resulting in a non-volatile content of 72% and a viscosity of 15p.
s (25°C), resin molecular weight 7001, hydroxyl group equivalent 135
A diisopropanolamine-modified epoxy resin was obtained.
Preparation and coating of two-component paint A paint was prepared using the diisopropanolamine-modified epoxy resin described above with the following formulation.

The equivalent ratio of hydroxyl group:isocyanate group is 1:1, that is, the component (A
)/component 1) in a weight ratio of 100/49 and stirred uniformly. The nonvolatile content is 76.2%, and the viscosity immediately after mixing is 2.
8 ps (25 is C), and the viscosity at -20°C was 81 ps. Next, I sandblasted 100x200x1.
The above mixed two-component paint was applied to a 6I iron plate at -20°C using an airless sprayer [Gray Co.'s Graco Hydro Cat was used: pressure ratio 50:1 (secondary pressure 200 kg/d, primary pressure 4
k9/CTil)].

The resulting coating film had a thickness of 100 μm. Table 1 shows the performance of the coating film. For the coating film performance shown in Table 1, each test was conducted using each top coat paint and after being left at the respective coating temperature for 7 days.

As shown in the table, all of the coating films obtained by the method of the present invention can be applied by a simple method in a low-temperature atmosphere even with a high non-volatile content, and the coating films have excellent performance. On the other hand, in Comparative Example 1, the molecular weight of the alkanolamine-modified epoxy resin was too large and the amount of non-volatile matter was too small, so a sufficient film thickness could not be obtained, and both corrosion resistance and physical performance were poor. In Comparative Example 2, because a normal epoxy resin was used, it cured slowly at low temperatures, requiring 84 hours to reach the level where it could be walked on.The test after one week showed that it had not completely cured, so the corrosion protection poor durability, moisture resistance, etc.
It was not practical. In Comparative Example 3, the coating film was brittle and had low physical strength due to the excessive isocyanate content.

Claims (1)

[Claims] 1. When painting steel structures in a low-temperature atmosphere of -20°C to +5°C, the mixing ratio of the following main components A and B is expressed as an equivalent ratio of hydroxyl groups: isocyanate groups. Te1:
0.5 to 1.5, and the nonvolatile content at the time of painting is 7.
A method for painting steel structures, characterized by forming a film thickness of 100 microns or more in one coating using a two-component paint containing 0% by weight or more. Component A: Alkanolamine-modified epoxy resin with a molecular weight of 650 or less. Component B: 2,2^1- or 2,4^1- or 4,4
^1-Diisocyanate diphenylmethane or modified products thereof. 2. The method of painting a steel structure according to claim 1, wherein an inorganic zinc primer is applied as a primer before applying the two-component paint. 3. The steel structure according to claim 1 or 2, wherein the alkanolamine-modified epoxy resin is an epoxy resin modified with diethanolamine or diisopropanolamine, and the two-component paint is applied by airless spraying or brushing. How to paint.